Section 2 Structure

2.1 Plans and data submissions

2.1.1 The following additional plans and information are to be submitted:

General arrangement plans of the drilling plant.
Drilling derrick structural plans and design calculations.
Raw water towers’ structural plans and design calculations.
Flares structures’ structural plans and design calculations.
Structural plans of equipment skids, support stools and design calculations.
Structural plans of supports to lifting appliances.

2.2 Materials

2.2.1 Materials are to comply with Pt 3, Ch 1, 4 Materials and material grades are to comply with Pt 4, Ch 2 Materials using the categories defined in this Section.

2.2.2 Support structures for the drilling plant are to be divided into the following categories:

Primary structure.
Secondary structure.

2.2.3 Main load-bearing members and elements subjected to high tensile or shear stresses are defined as primary structure. All other structure is considered to be secondary structure.

2.2.4 Some specific examples of structural elements which are considered as primary structure are as follows:

Derrick legs and base plates.
Derrick principal cross bearing.
Derrick crown block/water table supports.
Derrick bolts.
Support stools (attached to the main/upper deck).
Main legs, chords and end connections.
Foundation bolts.

2.3 Supporting structure interfaces

2.3.1 The design loadings for all structures supporting plant, including equipment skids, support stools, tanks and storage vessels, are to be defined by the designers/Builders and calculations are to be submitted in accordance with an appropriate Code or Standard, see Pt 3, Ch 17 Appendix A Codes, Standards and Equipment Categories.

2.3.2 The design of supporting structures for drilling facilities is to integrate with the primary hull under-deck structure.

2.3.3 The permissible stresses in the hull structure below the drilling plant are to be in accordance with Pt 4, Ch 5 Primary Hull Strength and the local strength is to comply with Pt 4, Ch 6 Local Strength.

2.3.4 The BOP frame, lifting points or supports are to meet the requirements of API RP 2A-WSD.

2.4 Derrick and masts

2.4.1 The structural design of drilling derricks is to be in accordance with a recognised Code of Practice, such as API Spec 4F or acceptable equivalent, see Pt 3, Ch 17 Appendix A Codes, Standards and Equipment Categories. The design conditions defined in Pt 3, Ch 7, 1.4 Plant design characteristics are to be complied with.

2.4.2 When the unit is to operate in an area which could result in the build-up of ice on the drilling derrick, the effects of ice loading are to be included in the calculations, see Pt 4, Ch 3 Structural Design. The design criterion for this condition may be taken as a non-drilling condition with defined setback loading. The environmental criteria are to be agreed with LR, but in general may be based on five-year return criteria for the operating location.

2.4.3 The structural design of the drilling derrick may be required by LR to include the effect of fatigue loading, see Pt 4, Ch 5 Primary Hull Strength.

2.4.4 Fatigue damage calculations for individual components when required are to take account of the degree of redundancy and also the consequence of failure.

2.4.5 Where National Administrations give specific requirements with respect to fatigue design, it is the responsibility of the Owners to comply with such Regulations.

The design of the derrick or mast and associated ancillary equipment is to incorporate features to reduce the risk to personnel during routine maintenance or operations.
The design is to allow for suitable and safe access from deck or installed work platforms for operation, maintenance and inspection services. All items in the derrick are to be accessible for routine inspection, without the need for man-riding winches.
Where direct access to lubrication points such as crown or deflector sheaves cannot be provided, the use of remote grease lines can be incorporated.
Portable equipment such as catwalk samson posts are also to be fitted with padeyes to allow safe removal and re-location.
The design is to also allow for extra hang off points for temporary equipment such as wire line units.
All padeyes are to be designed, installed and tested to LR requirements, and all padeyes are to be identified and a record book kept, allowing for inspection records to be maintained.
Consideration is to be given to providing access and means to fight a major fire at the monkey board level. The means to fight a fire at this level are to include portable and fixed fire-fighting systems.
Modification to any part of the derrick or mast from original design will require OEM and LR design approval, followed by trials if necessary.
Temporary installed structures, members or fittings are to undergo an assessment by the dutyholder to confirm they will not affect the original design; if the design is affected, details are to be submitted for approval.
Casing stabbing boards are to comply with the following requirements:
- The hoisting system is to be designed and constructed to Codes and Standards approved by LR.
- Permanent safe access to the stabbing board for operators and maintenance personnel is to be provided.
- Any rack and pinion system is to be designed so that the working platform will not fall if the rack or pinion should fail, and a single or common mode failure cannot occur.
- Where winch systems are used, the rope is to spool evenly on the drum and there are to be at least three full turns of rope remaining on the drum at all times.
- The rope is to remain captive with the drum and sheave systems under all service conditions, including slack rope conditions.
- Upper and lower-level limit switches are to ensure that the hoist system does not operate beyond its specified range.
- Casing stabbing boards is to be clearly marked ‘SUITABLE FOR CARRYING PEOPLE’ and with the number of people they can carry.
- Casing stabbing boards and other working platforms that are raised and lowered by a powered or manually operated system are to provide users with a secure and safe means of travel and support at the point of work.
- The working platform is to be positively guided by rails or runners. The guidance system is to ensure that the platform remains captive to its rails or runners under all circumstances, including any wheel or roller failure or failure of the primary hoisting system.
- Rails/runners are to be securely attached to their supports and are to not open up under static operations, travelling or other dynamic operations, overload testing or operation of the secondary control/braking system.
- The working platform is to have non-slip standing surfaces, handrails, mid-rails and edge protection.
- The platform is to also have anchorage points for inertia-type safety harnesses.
- Control of the primary lifting system is to provide smooth movement of the working platform. The control lever is to spring to neutral on release, effectively braking the primary hoisting system.
- Where a manual system of raising or lowering the platform is used, a positive locking system such as a ratchet-and-pawl mechanism is to be provided in addition to the service brake.
- A secondary, inertia-type brake, acting at the rails, is to be provided in case there is any failure in the primary hoisting system. The secondary brake is to act independently of the primary brake and not require any power source (hydraulic, electrical or pneumatic) for its operation.
- Each braking system is to be capable of holding the full rated capacity of the loaded stabbing board plus allowances for dynamic effects. It is not to be possible to lower the working platform by brake operation only. Two locking devices are to be provided, such that one locking device operates when the lifting handle is at neutral and the other one operates if the hoist mechanism fails. Each device is to be independent.
- A speed controlling device is to prevent the raising and lowering speed of the platform exceeding tripping speed.
- Adequate safety gear of the progressive type is to be provided, designed to engage within freefall conditions.
- The platform is to be equipped with a latch lock mechanism which secures it when not in motion.

2.5 Water towers

2.5.1 Water towers on self-elevating units are to be designed in accordance with a recognised Code or Standard, modified to take into account the unit’s motions and marine environmental aspects, see Pt 3, Ch 17 Appendix A Codes, Standards and Equipment Categories. Provisions for effective securing of towers when the unit is in transit is also to be similarly designed. The design conditions defined in Pt 3, Ch 7, 1.4 Plant design characteristics are to be complied with.

2.5.2 The structural design of the tower is to include the effect of fatigue loading, see Pt 4, Ch 5 Primary Hull Strength.

2.5.3 Where National Administrations give specific requirements with respect to fatigue design, it is the responsibility of the Owners to comply with such Regulations.

2.5.4 For slender structures and components, the effects of wind induced cross-flow vortex vibrations are to be assessed.

2.5.5 Wind loads are to be calculated in accordance with LR’s Code for Lifting Appliances in a Marine Environment (hereinafter referred to as LAME Code), or a recognised Code or Standard, see Pt 3, Ch 17 Appendix A Codes, Standards and Equipment Categories.

2.5.6 The permissible stresses in the hull structure below the tower are to be in accordance with Pt 4, Ch 5 Primary Hull Strength.

2.6 Flares structures

2.6.1 Flares structures are to be designed in accordance with the requirements of a recognised Code or Standard, see Pt 3, Ch 17 Appendix A Codes, Standards and Equipment Categories. The design conditions defined in Pt 3, Ch 7, 1.4 Plant design characteristics are to be complied with.

2.6.2 The flare structures are also to be designed for the imposed loads due to handling the structure and when in the stowed position.

2.6.3 The designers/Builders are to specify the maximum weight of the burner and spreader and the design criteria defined in Pt 3, Ch 7, 1.4 Plant design characteristics.

2.6.4 The structural design of flare structures is to include the effect of fatigue loading and the thermal loads during flaring, see Pt 4, Ch 5 Primary Hull Strength.

2.6.5 Where National Administrations give specific requirements with respect to fatigue design, it is the responsibility of the Owners to comply with such Regulations.

2.6.6 For slender structures and components, the effects of wind induced cross-flow vortex vibrations are to be assessed.

2.6.7 Wind loads are to be calculated in accordance with LR's LAME Code or a recognised Code or Standard, see Pt 3, Ch 17 Appendix A Codes, Standards and Equipment Categories.

2.6.8 Permissible stresses in the hull structure below the flare structure supports are to be in accordance with Pt 4, Ch 5 Primary Hull Strength.

2.7 Lifting appliances

2.7.1 Lifting appliances shall, as a minimum, meet the requirements of the following Standards and are to comply with LR’s LAME Code, and where applicable, PUWER Reg 4 and LOLER Reg 5. See also Pt 3, Ch 11 Lifting Appliances and Support Arrangements.

API Spec 2C. Specification for offshore pedestal mounted cranes.

API RP 2D. Operation and maintenance of offshore cranes.

ASME B30.20. Below-the-hook lifting devices.

BOP handling systems will meet the minimum requirements of API Spec 7K.

Hoisting appliances are to be located such as to ensure safe operation, and must be suitably protected if for location in a hazardous area. Protection is to limit surface temperature to a maximum of 80 per cent of auto-ignition temperature. This temperature, if unknown, may be taken to be a maximum of 200°C.

Submitted design data for hoisting appliances is to include all load and hoisting/lowering speed combinations at the rope drum.

Man-riding winches are to be of an approved type and certified for offshore use, and they are to comply with the following requirements:

Two fail safe brakes are to be provided, one automatic and the other manual.
Hydraulic winches may be provided with a regenerative brake system with breaking valve, in place of a secondary manual brake.
The operating lever is to be returned to neutral upon release in any position.
Declutching devices are not to be fitted, unless otherwise agreed by LR, see Pt 3, Ch 7, 2.7 Lifting appliances 2.7.1.
‘Sprag’ type unidirectional bearings (freewheels) are acceptable subject to regular satisfactory in-service inspection.
Lowering under normal operating conditions is to be through control of the motor.
Means for prevention of overriding and underriding of the winch is to be provided, where reasonably practicable.
Manufacturer’s label indicating operational parameters and approval for man-riding.
A sign affixed to the winch, clearly indicating suitability for man-riding (for example, ‘SUITABLE FOR MANRIDING’).
The winch operating lever must automatically return to neutral when released.
An automatic brake that will engage upon returning the operating lever to neutral.
A manual brake.
A guide for spooling the wire rope onto the drum (manual or automatic).
The ability to lower the rider in a controlled manner in the event of loss of power to the winch.
An emergency disconnect from the power source (ESD) located within winch operator’s reach.

2.8 Guard rails and ladders

2.8.1 It is the Owners’ responsibility to provide permanent access arrangements and protection by means of Ladders and guard rails. It is recommended that such arrangements are designed in accordance with a recognised Code or Standard.

2.8.2 Dutyholders should be aware that the hoops of a ladder alone may not be effective in safely arresting a fall without injury. Dutyholders are therefore advised to review their risk assessments and consider if additional fall protection is required or alternative means of access is to be supplied.

Where dutyholders choose to use fall arrest equipment inside a hooped ladder to arrest a fall, they should be aware that hoops may interfere with the operation of some types of fall arrest equipment (for example, inertia reel devices). Dutyholders should contact their manufacturer or supplier for advice on the performance of such equipment when used in a hooped ladder.

Users of fall arrest equipment inside a caged ladder should also be aware of the possibility of injury from striking the cage following a fall. The use of climbing helmets to reduce the risk of injury may need to be considered (refer to HSE CCID 1-2012).

Where ladders are used as (or part of) an emergency escape route, they are to be fire resistant to comply with BS 476 part 7, 1989 or equivalent.

Ladders fixed and portable are to be suitable for use in the intended areas, and the Owner is to conduct risk assessments with regard to the use of wooden or aluminium ladders in an offshore drilling environment.

2.9 Fire and blast loading

2.9.1 Particular consideration is to be given to the potential effects of fire and blast impinging on exposed boundary bulkheads of accommodation spaces and/or temporary refuge. Where boundary bulkheads can be subjected to blast loading, the scantlings are to comply with Pt 4, Ch 3, 4.16 Accidental loads and Pt 4, Ch 6, 9.1 General 9.1.6.

Other Standards which will apply to fire and blast loading include:

API RP 2FB Recommended practice for design of offshore facilities against fire and blast loading.